debian: enable automatic upgrades only for virtual machines

And factor out VM stuff into a separate file.

roles/debian/tasks/vm.yml

@@ -0,0 +1,12 @@
+- name: Install automatic upgrade package
+  package:
+    name: unattended-upgrades
+
+- name: Configure automatic upgrades
+  lineinfile:
+    path: /etc/apt/apt.conf.d/20auto-upgrades
+    create: yes
+    line: '{{ item }}'
+  loop:
+    - 'APT::Periodic::Update-Package-Lists "1";'
+    - 'APT::Periodic::Unattended-Upgrade "1";'